Current regulator for providing a constant output current in a telegraph loop



y 6, 1970 A. QUIROS 3,514,690

CURRENT REGULATOR FOR PROVIDING A CONSTANT OUTPUT CURRENT IN A TELEGRAPH LOOP Filed NOV. 17, 1967 III-J: l /e- PEGUL A 70/? IN VENTOR 44 144 90 Qu/eos BY 0 ATTORNEY United States Patent O CURRENT REGULATOR FOR PROVIDING A CON- STANT OUTPUT CURRENT IN A TELEGRAPH LOOP Alvaro Quiros, Springfield, Va., assignor to The Susquehanna Corporation, a corporation of Delaware Filed Nov. 17, 1967, Ser. No. 683,912 Int. Cl. G05f 1/ 44 US. Cl. 323--4 6 Claims ABSTRACT OF THE DISCLOSURE A two-terminal constant-current source for a telegraph loop. The regulator incorporates a diode bridge to make it polarity insensitive. Connected acrom the bridge is a high-gain circuit, one version of which is as a Darlington transistor pair. A Zener diode is placed at the input to the first transistor in the pair to provide a stable reference voltage. The output is taken from the emitter of the second transistor through a variable resistor which is used to set the desired current level. The use of the Darlington pair keeps the unregulated current, which is derived from the input circuit to the pair, to a very small percentage of the total regulator output.

BACKGROUND OF THE INVENTION This invention relates to a current regulator and more particularly to an adjustable current regulator for supplying a constant output current.

In the operation of telegraph signal loops, circuit and load switching can cause a change in loop current, absent regulation. The loop current, therefore, must be returned to its required level each time switching occurs. Rheostats are typical of the apparatus provided for the purpose of adjusting the current level in this situation. However, it is obvious that continuous adjustment of rheostats or the like is a most inconvenient and time-consuming practice, and that automatic current control would be a much more convenient technique and readily acceptable.

SUMMARY flows through this circuit. Clamping means at the input of the high-gain circuit provide a stable reference voltage for regulator operation. Unidirectional means steers current through the high-gain circuit in the same direction for bi-polar input signals.

An object of the present invention is to provide an improved current regulator which provides a constant current flow in a telegraph loop regardless of changes in loop supply voltage or load resistance.

Another object of the present invention is to provide such a regulator in which unregulated current is kept to a minimum value, constituting a minor percentage of total current flow.

Another object of the present invention is to provide such a regulator which is a two-terminal device requiring no external power supply.

Still another object is to provide such a regulator which is insensitive to the polarity of the loop supply voltage and can accommodate both neutral and polar signals.

Other objects and advantages will become apparent from a reading of the specification in combination with the accompanying drawing.

3,514,690 Patented May 26, 1970 BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagram of a system in which the regulator of the present invention can be used;

FIG. 2 is a schematic diagram of one preferred embodiment of the present invention;

FIG. 3 is a schematic diagram of a second embodiment of the present invention; and

FIG. 4 is a schematic diagram of another preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 there is shown a representative diagram of a polar telegraph loop having a keyer portion 10, load circuits 12, and a regulator 14 which is shown here as being positioned between the keyer and the load circuits. The keyer 10 is represented by a switch or relay which operates to apply either positive or negative battery to the telegraph loop. For example, for marking signals the relay contact 16 is connected to positive battery 18 and current flows from the positive terminal of this battery through the regulator 14, the load circuits 12, ground, and back to the negative terminal of this battery. For spacing pulses, the contact 16 is moved down into contact with the negative terminal of battery 20 and current flows from the positive terminal of this battery to ground, through the load circuits 12, regulator 14, and back to the negative terminal of this battery.

In a telegraph loop, it is preferred to operate load equipment 12 at a predetermined current level. However, if supply voltage such as the voltage at either or both of batteries 18 and 20 should vary, there is a resulting change in loop current. Also, as is often the case, if load equipment is switched into or out of the loop, the change in load resistance also causes a change in the loop current. Therefore, regulator 14 has been included in the loop to automatically maintain identical current magnitudes for both marking and spacing signals regardless of changes in the load resistance or in the supply voltages. As shown, regulator 14 is a two-terminal device which is connected in series in the loop circuit. The terminals have been designated A and B, one of which functions as an input terminal and one as an output terminal depending on the direction of current flow. The regulator 14 uses the voltage of the loop for its biasing and does not utilize a separate power supply.

In FIG. 2 there is shown a schematic diagram of a preferred embodiment of the regulator 14 of FIG. 1. Connected between the terminals A and B is a diode bridge circuit formed by diodes 30. The purpose of the diode bridge is to make the regulator insensitive to the polarity of the input signal. Thus, current is steered across the bridge in the same direction regardless of whether the input current enters at terminal A or at terminal B. With reference to FIG. 2, the current flow across the bridge is from line 32 to line 34 through the circuit components as hereinafter described.

Connected across the bridge is a large resistor 36 and a Zener diode 38. The junction of these two circuit components is connected to a high-gain device, which is also connected across the bridge. The high-gain device is formed of two transistors 40 and 42 arranged as a Darlington pair. The collectors 44 and 46 of these two transistors are connected to the top of the bridge at line 32. The emitter 48 of transistor 40 is connected to the base 50 of transistor 42. The base 52 of transistor 40 is connected to the junction of resistor 36 and Zener diode 38. The emitter 54 of transistor 42 completes the connection across the bridge for the Darlington pair through a resistor 56 of very low value and a potentiometer 58.

With reference now to FIGS. 1 and 2, assume that the telegraph loop is being supplied with -130 volts for the marking and spacing signals respectively, from batteries 18 and 20, and that potentiometer 58 has been adjusted for the fiow of a 50 ma. current through the loop. Within the regulator circuit 14 the Zener diode 38 is conducting and supplies a stable six-volt reference to the base 52 of the transistor 40.

With 6 volts at the input to the Darlington pair, there will be approximately 4.8 volts at the emitter 54 of transistor 42. Due to this stable voltage level at the emitter the current, as determined by resistor 56 and potentiometer 58, will stay at the constant current level selected at potentiometer 58, e.g. 50 ma.

Regardless of the change in the load resistance 12 the current in the loop, as controlled by regulator 14, remains substantially the same. For example, assume that there is a total of 20 volts drop across the load circuits 12 and that the supply voltage is at 130 volts. Ignoring other losses in the loop and with a 4.8 volt drop across resistor 56 and potentiometer 58, the remainder of the voltage drop in the loop occurs across the regulator circuit '14. This drop is found across the emitter-collector path of transistor 42 and approximates 105 volts.

Assume next that additional load is switched into the loop such that the total drop across the load circuits now equals 50 volts. There is no change at the emitter 54 of transistor 42 because that point is held at the stable 4.8 volt level due to the stable reference provided by the Zener diode 38. Therefore, a regulated 50 ma. constant current continues to flow in the loop. The remainder of the voltage drop between battery and ground is still to be found across the emitter-collector path of transistor 42, but this voltage drop now approximates 75 volts rather than the previous 105 volts.

Thus, the regulator circuit 14 will regulate the loop current over a wide range of load conditions. It has been found that for the values of resistance and voltage as sumed and shown in the figures the regulator can provide in the loop a regulated current between 20 ma. and to 100 ma. over a wide load range where the drop across the regulator varies from approximately 20 volts to 130 volts.

Likewise, if there is a variation in supply voltage, there is a change in the drop across the emitter-collector path of transistor 42. However, the voltage at the emitter, here by example being 4.8 volts, does not change, and the loop current remains constant.

It is preferred that the unregulated current be kept to a bare minimum since such current will aflect the efliciency of regulation over the wide range that the regulator is designed to operate. The Darlington pair is particularly effective in keeping the unregulated current, which flows in the path through resistor 36 and diode 38, to a low percentage of the total current, e.g. 1%5%. Normally, in a transistor the ratio of the emitter current to the base current is equal to the beta of the transistor. In a Darlington circuit this ratio is With reference to FIG. 2, the relationship between the input current applied to the base 52 of transistor 40 and the emitter current provided at the emitter 54 of transistor 42 is governed by the following formula:

As can be observed by selecting a reasonable value of 20 for 5, little base current is actually needed to drive the Darlington pair. Accordingly, resistor 36 can be made quite large, and is here selected to be 150,000 ohms.

Even with this large resistance there is sutficient current flowing through resistor 36, when the voltage drop across the bridge is small, to operate the Darlington pair and maintain the Zener diode 38 conducting. Selection of a low-current Zener, preferably in the microampere range, is helpful. Furthermore, when the voltage drop across the bridge is large, the high resistance of resistor 4 36 keeps the flow of current through the path of that resistor and diode 38 at a sufficiently low level such that the unregulated current never exceeds a small percentage of the total current derived from regulator 14. Thus, it can be said that substantially all of the regulator output current is derived from the Darlington pair.

A second embodiment of the present invention is shown in the schematic diagram of FIG. 3 where like parts have the same reference numerals as in FIG. 2. In this showing an emitter-follower is placed across the bridge between the Darlington pair 40, 42 and the path formed by resistor 36 and Zener diode 38. The emitter-follower is comprised of a transistor 70 and potentiometer 72. The base of the transistor 70 is connected to the junction of resistor 36 and diode 38, and this diode 38 establishes a stable reference voltage across the potentiometer 72. This potentiometer functions as a voltage divider, and the voltage selected by its tap and applied to the base of transistor -40 appears at the emitter of transistor 42, minus the voltage drop experienced across the two emitter-base junctions. The voltage at the emitter of transistor 42 across the resistor 56 determines the loop current, and thus the loop current is controlled by potentiometer 72.

The positioning of the potentiometer 72 in the emitterfollower circuit eliminates the requirement for a potentiometer which must accommodate large currents as in the case of potentiometer 58 in FIG. 2. However, the incorporation of an additional current path across the bridge means that more of the current in the total regulator output current is not controlled by the Darlington pair. However, it should be noted that the voltage at the emitter of transistor 70 is held at a stable level by the Zener diode 38; therefore, the current through this emitterfollower will be held at a fixed level, e.g. one ma., and can also be considered a regulated current.

A third embodiment of the regulator 14 is shown in the schematic diagram of FIG. 4 wherein like components have the same reference numerals used in FIG. 3. In this embodiment, a pair of transistors is again connected as a high-gain circuit, but a Darlington arrangement is not employed.

Transistor has its collector 82 connected to the base 84 of transistor 86, which is of opposite conductivity to transistor 80. The base 88 of transistor 80 is connected to the tap of potentiometer 72, and the emitter 90 of transistor 86 is connected to the top of the bridge. The collector 92 of transistor 86 and the emitter 94 of transistor 80 are commonly connected at junction 98 to one side of the constant-current-determining resistor 56.

A small resistor 96 is connected between the top of the bridge and the junction of collector 82 and base 84, and provides a path for leakage current from the base of transistor 86 in order to suppress the tendency of this transistor to conduct excessively under high temperature conditions. The use of PNP transistors 70 and '80 requires a reversal of polarity of diodes 30 and 38. Conventional current flow is now from the bottom to the top of the bridge.

Diode 38 again establishes a stable reference voltage across potentiometer 72. The input voltage to base 88 of transistor 80 is provided by the potentiometer tap. This, too, is a stable reference voltage and it also appears at the junction 98 because transistor 80 is constructed as an emitter-follower. This voltage across resistor 56 gives a constant current for the regulator 14 to apply into the loop. The major current path through the regulator is from the bottom to the top of the bridge through resistor 56 and the collector-to-emitter path of transistor 90. A small amount of current also flows from junction 98 into transistor 80 to provide base current and collector current.

However, it should be noted that these are also regulated currents because the branching currents at junction 98 form the total constant current through resistor 56.

Assume that it is desired to increase loop current. The setting of potentiometer 72. is increased, raising the voltage at the base 88 of transistor 80. This transistor senses the voltage difference between its base and emitter and injects an increased current from its collector 82 into the base 84 of transistor 86. Transistor 86 conducts more heavily and more current flows through its emitter-collector path. The voltage at junction 98 begins to increase and continues until it reaches the level of the base 88 of transistor 80 (minus the drop across the transistor junction). The new stable voltage level at junction 98 establishes a new constant current output for the regulator 14.

'During the rise in voltage at junction 98, the base current into transistor 86 was progressively decreased as transistor 80 sensed a reduction of voltage diiTerence between its base and emitter. Accordingly, the conduction of transistor 86 tapered off. Once the new voltage level was attained, sufficient base current was flowing into transistor 86 to hold it at the necessary conduction level such that junction 98 is retained at its new voltage level.

For a decrease in the constant current of regulator 14, the opposite effects occur. Potentiometer 72 is decreased putting the voltage on base 88 below the emitter 94 of transistor 80. Transistor 80 reacts by reducing the base current of transistor 86. Transistor 86 reduces its conduction and junction 98 begins to drop towards the voltage level at the base of transistor 80. Eventually, the new voltage levels are again balanced across the base/emitter junction of transistor 80. The new stable voltage reference at junction 98 establishes a new, but lower, constant-current through resistor 56.

As described, transistor 80 can be regarded as a comparator which compares the voltages at its base and emitter and controls the conduction of transistor 86. Transistors 80 and 86 also function as a high-gain circuit, the same as the Darlington pair in the embodiments of FIGS. 2 and 3. For example, with the circuit values shown and 100 ma. flowing through the collector-to-emitter path of transistor 86, the base current of transistor 80 is about .1 ma., a ratio of 1000zl. Again, a large resistor 36 can be selected and the unregulated current through this resistor and diode 38 is thereby kept to a small percentage of the total output current.

It has been found that the circuit of FIG. 4 is less sensitive to changes in loop load conditions than the regulator circuits of FIGS. 2 and 3, depending upon the quality of the transistors used in the Darlington circuit. The B of certain transistors which can be used in forming the Darlington pair may vary depending upon the collectorto-emitter voltage of the current-carrying transistor. This voltage, as previously explained, changes with load conditions in the loop. Too large a variance in B between the extreme ends of possible load conditions can cause undesirable variations in the level of the regulated current. The circuit of FIG. 4 makes a uniform [3 for the currentcarrying transistor, here transistor 86, no longer critical. Should the current through this transistor begin to change because of changes in loop load conditions, the voltage at junction 98 will also begin to change (rise or fall). Transistor 80 now senses a voltage difference between its emitter and fixed base reference, and varies the base current into transistor 86 sufiiciently to return junction 98 to the proper level. Accordingly, the current through transistor 86 returns to its proper level, and the constant-current output of the regulator 14 is retained.

While the present invention has been described with regard to a polar telegraph system, the invention works equally as well with neutral systems, such systems being Well represented in the art.

There have been described three specific embodiments of the present invention, but these are merely illustrative of other embodiments that may also be within the scope of the invention.

What is claimed is:

1. A current regulator for providing a constant output current in a telegraph loop comprising, one input terminal and one output terminal, said two terminals beingadapted to connect the regulator in series in said telegraph loop, a high-gain circuit connected between said two terminals, substantially all of the output current provided by the regulator being derived from said highgain circuit, an emitter-follower circuit having at its output a variable resistor including a tap, said tap being connected to the input of said high-gain circuit and in combination with said variable resistor serving to set the output current to a desired level, clamping means connected to said emitter-follower circuit for holding the input voltage for said high-gain circuit at a stable level to cause said high-gain circuit at a stable level to cause said high-gain circuit to function in a constant current mode, and unidirectional means connected to the input and output terminals for steering current through the high-gain circuit in the same direction in the presence of input signals of either polarity.

2. A current regulator as claimed in claim 1 wherein the high-gain circuit includes a Darlington transistor pair, said tap being is connected to the first transistor of the pair and the output current being derived from the second transistor of the pair.

3. A current regulator as claimed in claim 2 wherein said transistors in said Darlington pair each have base, collector and emitter electrodes, the collectors being connected together at the input terminal, the emitter of the first transistor being connected to the base of the second transistor, and the emitter of said second transistor being connected to said output terminal, and wherein said tap is connected to the base of said first transistor, and said clamping means is a Zener diode.

4. A current regulator as claimed in claim 1 wherein the high-gain circuit includes a pair of transistors of opposite conductivity, the first transistor in said pair being connected to said tap and controlling the conduction of the second transistor in said pair.

5. A current regulator as claimed in claim 4 wherein the transistors in said pair each have base, collector and emitter electrodes, the collector of the first transistor being connected to the base of the second transistor, and the emitter of the first transistor being connected to the collector of the second transistor at a common junction.

6. A current regulator as claimed in claim 5 further comprising a resistor connected between said common junction and said input terminal, said tap being connected to the base of the first transistor in the pair, said first transistor serving to maintain the voltage which appears at said junction substantially equal to said input voltage by controlling the conduction of said second transistor, thereby to maintain constant current across said resistor.

References Cited UNITED STATES PATENTS 4/1966 Herz 323-4 3/1968 Shapiro 323-4 US. Cl. X.R. 323-38, 39; 325l86 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 514, 690 Dated 26 May 1 970 Inventor(s) Alvaro Quiros It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

1 Claim 1 line 15: Delete "at a stable level to cause said".

2. Claim 1 line 16: Delete "high-gain circuit" n fl u SEALER SEAL) Eamannmm, NIH-1M1!- JR.

Gemissiom of Patents ORM PO 1050 "o 69 USCOMM-DC 60376-969 n U S GOVEINMINY FHINHNQ OFHCS I969 i" 56 

